Combined direct resistance heating and voltage cancellation system



Feb. 11,- 1969 Q Q TRAUTMAN ETAT.` 3,427,430

COMBINED `DIRECT NEsIsTANcE HEATING AND VOLTAGE CANCELLATION SYSTEM Filed Dec. 17. 1965 QI Q\ t Q g1 rNVENToRs OSCAR c. rRAurMA/v "N N CL/FFORD f.' M0060 I ATTORNEYS United States Patent 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus for heat treating continuously moving wire strapping and the like consisting of a conductive bath and a grounded quench bath for electrically contacting the wire at spaced locations. A distributed open core transformer prior to the conductive bath provides voltage for effecting a difference in potential between the baths and thus, heating of the wire by the direct resistance method. The wire passes through the open cores of the transformer and has a voltage induced therein equal and opposite to the bath voltage so that voltage cancellation occurs and the remainder of the wire is reduced to ground potential.

Disclosure This invention relates to the direct resistance method of heating wire, steel strapping and the like in a continuous operation and more particularly to apparatus for eliminating the safety hazards of the operation.

In the past it has been the practice to use either a twocontact or three-contact arrangement for applying the voltage to the wire or strapping. In the three-contact arrangement, the critical heating takes place between the second and third contacts with a preheat zone between the iirst and second contacts. Here it is convenient to ground both the first and third contacts and apply the live voltage at the second contact. The supply drum leading material to the first contact m-ay be grounded as also may the takeup reel receiving material from the third contact. Thus the heating operation may be completely isolated and no open voltage or potential hazard to operators will exist. However, this system requires the use of a third contact bath with the inherent problems of maintaining a good electrical contact and maintaining the baths at the proper temperatures, together with the necessity of a center-tapped transformer, which is expensive and unwieldy.

It is more usual in these systems to use a two-contact operation and apply the voltage between the first contact bath and the second contact bath which is also a quench bath and is usually grounded. In this arrangement the supply reel is at substantially the same potential as the rst contact bath. It is usual practice to support the supply reel on a wooden platform 0r in some other way isolate the reel so that there is no leakage current flow. Here operators handling the reel, to be safe, must remain on the platform and are constantly exposed to an open voltage potential.

An object of this invention is to provide apparaus for eliminating the electrical shock hazards in such two-contact resistance heating operations.

Another object is to generate an electrical voltage equal and opposite to that occurring in the portion of the wire between the supply reel and the direct resistance heating area so as to cancel the voltage appearing in this portion and permit the supply reel as well to be grounded.

Still another object is to generate this voltage by using the same transformer assembly which supplies the current to the direct heating portion so as to automatically compensate for voltage fluctuations.

Patented Feb. 11, 1969 ice Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth-in detail certain illustrative embodiments of the invention, these being indicative, however, of but several of the various ways in which the principles of the invention may be employed.

In said annexed drawings:

FIG. l is a schematic elevational view of a direct resistance heating system showing the inclusion of voltagecancelling apparatus in accordance with the present invention; and

FIG. 2 is a schematic end View of a transformer used in the invention showing steel strapping passing through an aperture of the transformer.

Referring to the drawings and to FIG. 1 in particular, there is shown a schematic representation of the two-contact direct resistance heating system. Steel strapping 1, which may also be a group of wires, plural lengths of strapping and the like characterized by the ability to conduct electrical current, is shown as a continuous line passing from left to right guided by sheaves 2-8. The strapping 1 emanates from a supply drum (not shown) and passes in the direction of the arrow toward the conductive sheave 2 and is stored on a takeup drum (not shown) after leaving sheave 8. Elevated sheaves 3 and 6 and sinker sheaves 4 and 5 together are arranged to guide the strapping into and out of the rst contact bath 9, which consists of a container that is electrically conduc- .ive and contains an electrically conductive liquid such as heated lead, lead salts and the like. Sinker sheaves 7 and 8 guide the further advance of the strapping 1 to a second contact bath 10, which is similar to the first bath but also serves as a quench for the heated strapping, the span between the two baths preferably being enclosed by a housing 11. Both contact baths 9 and 10 are usually kept at elevated temperatures to liquify the conductive medium carried therein and also in the case of bath 10 to provide the proper quenching temperature. The temperatures of these baths however, are low in relation to the temperature of the heated portion 12 of the strapping between the baths.

A source of voltage is applied to the first and second contact baths by way of leads 13 and 14 and causes a current flow in the portion 12 of the strapping 1 between the first and second baths. A transformer assembly 15 energized from a power source 16 transforms the voltage to a suitable level for application to leads 13 and 14. Voltage source 16 is an AC power supply variable over the approximate range of 0-550 volts and may be varied to supply the necessary voltage to leads 13 and 14` required for different types or quantities of materials to be subjected to heating.

In this embodiment, transformer assembly 15 consists of a plurality of transformers 17 whose primary Iwindings 18 may be connected in parallel to the power source. Secondary windings 19 are connected to form a single secondary winding which supplies the voltage to the two contact baths. As seen in FIG. 2` each individual transformer 17 consists of primary and secondary windings on a core which has an aperture or window 20 therein. The transformers are aligned so that the strapping may pass through these apertures and be subjected to the magnetic field appearing therein for the purpose to be described hereinafter. The secondary windings may be connected in series, parallel or series-parallel configuration to also provide the proper operating voltage on leads 13 and 14.

The voltage applied between the first and second contact baths thus causes a current tiow through the portion 12 of the strapping between these points and a subsequent heating thereof due to the resistance of the material to the flow of current. IIn the usual mode of operation the second Contact bath is at ground potential, and the first Contact bath is at the potential of the secondary of the transformers, usually on the order of up to 150 volts.

Thus it can be seen that the portion of the strapping before the first contact bath is also substantially at this same potential and presents a shock hazard to an operator or at least a source of leakage current. It is desirable to be able to maintain this portion of the material also at ground potential or at least be abley to isolate this portion to prevent the shock hazard. 1t has been determined that a voltage can be induced in this portion of the wire through the action of transformer 15 in such a manner as to oppose the voltage appearing in this portion due to the potential applied at the first and second contact baths. Therefore, if the transformer 15 is interposed between sheaves 2 and 3 as near as is physically possible to the first contact bath, then the voltage appearing on the strapping before this zone and at the point of sheave 2 will be at zero potential. The voltage having been thus cancelled, conductive sheave 2 may be connected to ground potential as by lead 21. It can be seen that the secondary windings 19 may be selectively interconnected so that the voltage appearing between the contact baths is equal to the voltage induced in the strapping before the first contact bath so that the resultant voltage at sheave 2 equals zero.

In actual practice, however, because the transformers secondaries provide definite quantities of voltages, it is often impossible to so interconnect the windings to cause Complete cancellation. fFor this reason a separate trimming inductor 22, having an aperture through which the strapping passes, is located near and ahead of the transformer assembly 15. lInductor 22 has only a single winding and receives its energization from a Variac 23 or other suitable voltage changing device. In this embodiment Variac 23 is also connected to voltage source 16 so that it will reliect fluctuations in the same line voltage. Howe-ver, because the voltage contributed by the trimming inductor 22, is rather small, the Variac 23 may be connected to an independent power source without appreciably changing its effect. It is important to have the voltage in the strapping at sheave 2 as close to Zero as possible to prevent current iiow through sheave 2 to ground and the subsequent pitting and imperfect minor surface hardening of the wire.

In a typical operating arrangement of this invention the source voltage 16 may be adjusted to provide 150 volts at each of the secondaries 19 of the transformer. With the secondaries connected in parallel as shown in the drawing this would provide 150 volts to the lead wires 13 and 14. However, because of the heavy load due to the low resistance of the strapping between the contact baths 9 and 10, the Voltage actually supplied is substantially lower than this and it is this lower voltage which must be cancelled in the initial length of strapping in order to permit grounding at sheave 2. As previously described, trimming inductor 22 may provide up to about 15 volts of cancellation, if necessary.

The strapping passing through the transformer assembly 15 is subject to the magnetic field of the transformer and has a voltage induced therein which by appropriate connection is opposite in phase to that applied at the contact baths. TheA looseness of the magnetic coupling between the transformer and the strapping does not prevent induced voltage sufficient for the purpose and is not detrimental to the operation of the system.

It is also seen that transformer 15 may be of any suitable configuration just so `long as it supplies the necessary voltage for the desired heating. Thus it may be a single transformer core with single primary and secondaryV windings with provision for passing wire or strapping through its magnetic field. llt is only necessary to provide suliicient flux linkages between the transformer and material to generate the required cancelling voltage.

It is also possible to employ separate devices for applying potential to the contact baths and for inducing a cancellation voltage. A separate inductor coiled about the input portion of material could be used to supply the necessary cancellation voltage. However, this will not provide the automatic equal cancellation of voltage fluctuations that are inherent in the described singletransformer systems.

The inherent advantage in using the same transformer to supply both the voltage to the contact baths and the cancelling voltage induced in the wire is believed obvious. Fluctuations in the voltage from the power source are nullified in that they appear both at the direct resistance heating portion and at the induced voltage portion of the material. lFurther, there is a substantial cost savings relalized in using only the single transformer assembly.

Other modes of applying the principles of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equi-valent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. Apparatus for heat treating wire strapping material and the like through which the material is advanced from supply means to takeup means, comprising first and second contact means engaging the material at spaced locations to define a heating zone, electric means for heating the material in such zone comprising a power transformer having a primary winding connected to a source of energy and a secondary winding connected to said first and second contact means, means for electrically grounding one of said contact means whereby the material outside the heating zone at the side of said one contact means is at ground potential, and means for directing the material outside the heating zone at the side of the other said contact means, through the magnetic field of the transformer to induce therein an equal and opposite voltage to that at said contact means to cancel the voltage in the material.

2. Apparatus as set forth in claim 1 wherein said transformer comprises a magnetic core having an aperature therein, the primary and secondary windings of said transformer being wound on said core and the material to be treated being directed through such aperture.

3. Apparatus as set forth in claim 2 wherein said transformer comprises a plurality of open core transformers, distributed along a length of the material to be treated, adjacent the heating zone, said plurality of transformers having primary windings energized from the power source and secondary windings interconnected to provide a desired voltage for application to said first and second contact means.

4. Apparatus as set forth in claim 3 further including an inductor magnetically coupled to the material and associated with said plurality of transformers and means for adjustably energizing said inductor to induce additional trimming voltage in the material to reduce the voltage to ground potential.

References Cited UNITED STATES PATENTS 2,658,982 11/1953 Rendel 219-l55 RICHARD M. WOOD, Primary Examiner. BARRY A. STEIN, Assistant Examiner.

U.S. Cl. XR. 219-50 

